Cao Teng serves as a eunuch in the Han imperial court, holding the position of Central Regular Attendant and Empress's Chamberlain under Emperor Huan. His political influence involves the controversial practice of selling official positions. He adopts Cao Song, the future father of Cao Cao, making Cao Teng Cao Cao's adoptive grandfather.

As grandfather to Cao Cao, Cao Teng provides protection and mentorship during his upbringing. He displays fierce loyalty, confronting Emperor Ling to indirectly accuse the powerful eunuch Zhang Rang of corruption and moral failings. During this audience, with Zhang Rang present beside the emperor, Cao Teng boldly demands Zhang Rang's execution. Privately afterward, Cao Teng warns Zhang Rang that harming Cao Cao would ensure their mutual destruction.

Cao Teng holds the peerage title of Marquis of Fei. His political acumen and willingness to challenge corrupt figures like Zhang Rang significantly shape Cao Cao's early development and understanding of court dynamics. The series portrays him as a protective figure whose actions directly impact Cao Cao's path through the treacherous Han court.

His death occurs before the major events of the Yellow Turban Rebellion and the rise of regional warlords, though his influence persists through Cao Cao's career. Historical sources note his service during Emperor Huan's reign and his role in the Cao family's ascendancy, which the series incorporates.